The present invention relates generally to a microstrip structure for electromagnetic signals in the microwave frequency range and higher, and more specifically to a microstrip distribution network and/or microstrip antenna, for example a base station antenna for a mobile telephone/communication system.
Microstrip antennas with microstrip distribution networks are traditionally manufactured in the form of boards in a dielectric material made from fibre glass epoxy, fibre glass reinforced PTFE (PTFE--Polytetraflouroethylene--teflon), or the like. These types of dielectrics are usually used because they commonly also act as a carrier for the ground plane and the relevant conductors. From an electrical point of view it would be preferable to have air or vacuum as a dielectric, but that would make mounting of a ground plane at a predetermined and fixed distance from conductors extremely difficult and expensive, if at all possible. Therefore the industry traditionally uses substrates made of fibre glass epoxy, fibre glass reinforced PTFE, or the like, as a compromise between different mechanical and electrical parameters. These dielectrics/carriers have in common that they are made of organic materials which often comprise flourides and/or anti-flame protection with bromides due to a low flame point of the materials. A problem with these dielectrics/ carriers is that they do burn even though they are treated with environmentally unfriendly anti-flame protection. Bromides and/or flourides can be released into the environment when the dielectrics burn. Flourides and bromides are considered to be extremely environmentally unfriendly. Due to the large number of base station antennas in mobile telephone networks, large amounts of bromides and/or flourides can be released into the environment when these antennas are destructed due to replacement or a fire.